Polypropylene glycols (PPG), especially ethylene oxide (EO) capped PPG's, are the most commonly used polyether soft segment in RIM processing. The EO capping provides primary hydroxyl groups on the PPG, which (if uncapped) contains basically secondary hydroxyl groups. Capping thereby increases the reactivity of the parent PPG. High reactivity is a prerequisite in a RIM process.
A RIM composition (like polyurethane elastomers in general) is composed of a soft segment (derived from the aforementioned polyether) and a hard segment resulting from the reaction of a chain extender (usually a low molecular weight diol or polyol such as 1,4-butanediol, ethylene glycol, etc.) and the diisocyanate. The concentration of the hard segment governs the hardness of the final product. At a given hardness, each individual component has an effect on the overall properties, such as tensile strength, elongation at break, weatherability, etc.
There are many grades of PPG in the market, differing in functionality, molecular weight (or equivalent weight), degree of EO capping, etc. Each one may show some difference in RIM processing behavior as well as physical properties in the final product. A polyether having an equivalent weight (eq. wt.) of 1000 or higher usually gives good molding characteristics.
U.S. Pat. No. 3,963,681 discloses a polyurethane elastomer composition having improved static mechanical properties made from a polyfunctional isocyanate, curing agent and polyether. The weight average molecular weight of the polyether is within the range of 1,000 to less than 4,500. Also, the molecular weight distribution curve of the polyether has at least two peaks. At least one peak is located in the higher molecular weight region and at least another one is located in the lower molecular weight region relative to the rheological critical molecular weight of the polyether. According to the patent, to obtain the improved properties of the compositions, one of the essential factors is the use of polyethers having the particular molecular weight range described (see, for example, the paragraph bridging Columns 3 and 4, and paragraphs 1 to 3 of Column 4).
U.S. Pat. No. 4,242,463 relates to a color stable integral skin polyurethane foam. The polyurethane is prepared by reacting: (a) a polyol; (b) an isocyanate selected from the group consisting of aliphatic or cycloaliphatic isocyanates; (c) a crosslinker; and (d) a catalyst comprising stannous octoate and dimethyltin dilaurate. It is disclosed that the polyol used should be selected from the group consisting of polyether polyols which are polymer products of organic oxides. The two organic oxides used for most polyether polyols are ethylene oxide and propylene oxide. Among the examples of chain extenders disclosed is 1,4-butanediol.
U.S. Pat. No. 4,261,877 discloses a polyurethane composition, castings of which reportedly have high strength. The composition results from the reaction of a polyisocyanate with a blend of polyether polyols. A major portion of the blend comprises polyether polyols selected from the group consisting of those having a hydroxy number of 400 to 1000 and a functionality of 3-4. A portion of the blend, effective to improve substantially the strength of the blend, comprises a graft polyol which is liquid and pourable at ambient temperature. The graft polyol is a product of the free-radical-catalyzed polymerization of at least one ethylenically unsaturated monomer with a polyol which contains carbon-carbon unsaturation and oxyalkylene moieties and which has an average molecular weight on the order of 300 to 10,000.
U.S. Pat. No. 4,350,778 discloses a method for making a polyurethane elastomer reportedly having significantly improved properties. In the method an aromatic polyisocyanate, a polyol of above about 500 equivalent weight, a chain extending agent and a catalyst system is injected via a RIM machine into a mold cavity of the desired configuration. The chain extending agent comprises a low molecular weight active hydrogen containing compound of at least 2 functionality. The catalyst system is N-hydroxypropyl-N', N', N", N"-tetramethyliminobispropylamine, dibutyltin dilaurate and an alkyltin mercaptide. The polyols which are useful include polyether polyols, polyester diols, triols, tetrols, etc., having an equivalent weight of at least 500, and preferably at least 1000 up to about 3000.
U.S. Pat. No. 4,350,779 discloses a method for making a polyurethane elastomer reportedly having significantly improved properties. In the method an aromatic polyisocyanate, a polyol of above about 500 equivalent weight, a chain extending agent and a catalyst system is injected via a RIM machine into a mold cavity of the desired configuration. The chain extending agent comprises a low molecular weight active hydrogen containing compound of at least 2 functionality. The catalyst system is methyldiethanolamine, dibutyltin dilaurate and an alkyltin mercaptide. The polyols which are useful include polyether polyols, polyester diols, triols, tetrols, etc., having an equivalent weight of at least 500, and preferably at least 1000 up to about 3000.
U.S. Pat. No. 4,440,705 relates to the preparation of cellular and non-cellular polyurethane elastomers. In particular, this patent relates to the use of polyoxyalkylene polyether polyols containing an ethoxylation degree of 1 through 13 and a primary hydroxy group content of up to 100 percent for the preparation of polyurethane elastomers.
U.S. Pat. No. 4,438,248 discloses a process for preparing a non-cellular polyurethane elastomer. The process comprises reacting, in the absence of a blowing agent, an organic polyisocyanate with an organic compound having at least two Zerewitinoff active hydrogen atoms in a ratio of from 1.0 to 1.2 equivalents of isocyanate groups per equivalent of active hydrogen atoms in the presence of a catalytically effective amount of a co-catalyst composition. The co-catalyst composition comprises an organo-mercuric compound and an alkali metal carboxylic acid salt. The co-catalyst composition components are in a weight ratio of from 1 to 5 parts organo-mercuric compound per part of alkali metal carboxylic acid salt.
A welcome contribution to the art would be a polyurethane composition which does not require multi-component catalyst systems or grafted polyols to produce such a composition with good tensile and elongation properties. Preferably, such a composition would be suitable for a RIM process. Such a contribution is provided for by this invention.